Envelope-to: dave@picks.force9.co.uk
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Date: Tue, 17 May 2005 12:26:40 -0700
From: "Scott Tilley, VE7TIL" <sthed475@telus.net>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: CORES
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Mal

#3 still has atleast enough inductance to have a reactance 4-5 times that of 
reflected resistance of a typical xfmr used in LF setups... Imagine the two 
impedances in // as the inductive reactance increases on the smallest winding 
it has less and less of an effect on the system... I would imagine that your 
resistance on the drive side is lower then 3 ohms and your inductive reactance 
would be in the 20 ohm range which is well within typical folklore for 
building such a beast... The best situation would be to choose one of the 
cores for the least number of turns needed to setup the match and still 
maintain an inductive reatance on the smallest winding of atleast 4 times the 
desired reflected resistance... The latter produces the most effecient system 
due to skin effect losses... Watch for saturation with the street ferrite as 
you hammer it hard... 

You're into the hair splitting realm...  

73 Scott

Quoting hamilton mal <g3kev.ham@virgin.net>:

> I have been winding some transformers recently and have been getting some odd
> results.
> All cores have a prim of 9 turns and 27 turns sec.
> 
> 1. 3C85 58 mm diam Prim inductance 167uh Sec 744 uh
> 2. Same material abt same size but E core Prim 292 uh Sec 2810 uh no gap.
> 3. Material unknown out of a smps similar size Prim 21 uh Sec 178 uh no gap
> 4. TV lopt core again abt same size Prim 79 uh Sec 865 uh no gap
> 
> The Prim wire is litz 2mm and sec 1mm copper enam wire in all cases.
> 1 and 2 seem to have a big difference considering the same material, 3 must
> have a low u.
> Has anyone else tried comparisons of cores.
> If cores are selected at random and not checked there would be a big
> variation in results even using the same turns ratio.
> The above are intended as output matching transformers in the FET amps like
> the YXM and MRF class D/E design.
> I normally use 1 in my amps but have tried 3 and in spite of the big
> difference in values it does seem to work and I have not noticed any
> difference in RF output, which seems strange.
> 73 de Mal/G3KEV
> 
> 
> 
>  
>